Refrigeration systems typically operate by evaporating and condensing a refrigerant to achieve cooling. A wide variety of refrigerants and refrigeration systems are available for private and commercial use, including refrigeration systems using a halocarbon refrigerant.
Typically during a refrigeration cycle, the refrigerant is circulated through an evaporator in which the refrigerant boils at a low temperature to produce cooling. The refrigerant passes from the evaporator to a compressor that increases the pressure and temperature of the gaseous refrigerant and subsequently to a condenser in which the refrigerant discharges its heat to the environment. The refrigerant then flows from the condenser to an expansion valve. Here the refrigerant liquid expands from the high pressure level in the condenser to the low pressure level in the evaporator, and the cycle is completed as the refrigerant returns to the evaporator.
During the course of this cycle, the refrigerant can often become contaminated with a variety of non-condensible gases, including air and water. Such contaminants interfere adversely with the operation of refrigeration systems. When contaminants are present in the system, higher condenser pressures with accompanying increased power costs are required to operate the refrigeration system. Therefore the presence of contaminants in refrigeration systems decrease the efficiency of the operation of such systems. Contaminants in the system also reduce the capacity of refrigeration systems by displacing refrigerant vapor and increasing the pressure against which the compressor must operate in the case of a centrifugal compressor. Further, the presence of such contaminants may lead to the formation of acids resulting in corrosion of internal refrigeration machine components. To counter the effect of such contaminants, purge systems have been developed and incorporated into refrigeration systems to remove or "purge" the non-condensible gases and other contaminants from the system.
Conventional purge systems remove contaminants by directing a small stream of refrigerant vapor, laden with air and other contaminants, into a purge chamber which is separate from the refrigeration condenser and evaporator. Typically a heat transfer coil is used to condense the refrigerant by providing the coil with cold water, air or cooled refrigerant. The refrigerant is condensed within the purge chamber and directed back to the refrigeration machine, and a purge stream of contaminants is discharged to the atmosphere.
The discharge, however, often still contains a substantial amount of refrigerant, which is also discharged to the atmosphere. All purges relying on condensing coils to separate refrigerant from non-condensables suffer several limitations, both physical and practical. Condensing refrigerant from a non-condensible is controlled by temperature and pressure. As temperature is lowered and pressure increased, more refrigerant can be condensed. Practical limitations on producing a cold sink, and pressure limitations resulting from refrigerant breakdown at high pressure limit the amount of refrigerant that can be ultimately removed from a refrigerant/contaminant mixture. In view of increasing environmental awareness of the effect of some refrigerants on the ozone layer, efforts have increased to reduce the release of these type of compounds into the atmosphere. Further, it would be advantageous economically to separate and reuse the refrigerant to provide a more efficient and cost-effective refrigeration system.
Various means for increasing the efficiency of refrigeration systems have been proposed. For example, U.S. Pat. No. 4,304,102 discloses a refrigeration purging system with a secondary purge chamber for the removal of non-condensible gases. A portion of refrigerant is placed in a first purge chamber with a condensing coil where refrigerant and condensible contaminants such as water are condensed, leaving non-condensible gases such as air and a portion of the refrigerant at the top of the chamber. The refrigerant/non-condensible gas mixture is passed from the first chamber to a second purge chamber with a second condensing coil. Here the remaining refrigerant is condensed and returned to the first purge chamber, and the non-condensible gases are released to the atmosphere. Despite the use of two condensing coils, however, the same limitations that affect the efficiency of a single condenser purge system remain, and thus practically only a limited amount of refrigerant can be removed due to partial pressures exerted by refrigerant/air mixtures.
U.S. Pat. No. 4,984,431 discloses a purge system which includes a purge chamber with a condensing coil. A mixture of refrigerant and non-condensible gases is directed to the purge chamber where the mixture is cooled by the condensing coil. An amount of refrigerant is separated from the non-condensible gases, and the non-condensible gases and remaining refrigerant are routed from the purge chamber to a filter tank. The filter tank is filled with an adsorbent carbon material which adsorbs refrigerant remaining in the mixture. The remaining non-condensibles and refrigerant are then vented to the atmosphere. This system requires the periodic removal and replacement of the carbon material as it becomes saturated.